Discord: Fix GetUsers, add invite messages

The "Send to" box on the invite tab now accepts username#discriminator,
and a search icon has been added which opens a search window similar to
the one on the accounts tab. DiscordDaemon.GetUsers was also very broken
and wouldn't work with full username#discriminator, that's been fixed.

ts/typings/d.ts

@@ -109,7 +109,7 @@ interface Invite {
     code?: string;
     expiresIn?: string;
     remainingUses?: string;
-    email?: string;
+    send_to?: string;
     usedBy?: { [name: string]: number };
     created?: number;
     notifyExpiry?: boolean;